Device and method for electrochemical reduction

ABSTRACT

A device for electrochemical reduction of a workpiece ( 10 ) includes a workpiece ( 10 ), an electrode ( 20 ), and an electrolyte ( 30 ), which is located between electrode ( 20 ) and workpiece ( 10 ). The electrode ( 20 ) is moved close to the workpiece ( 10 ) with a small gap dimension ( 21 ), and a processing of the workpiece ( 10 ) occurs through a flow of current between electrode ( 20 ) and workpiece ( 10 ) through the electrolyte ( 30 ). In addition, a sonotrode is positioned to introduce sound waves.

Priority is claimed to German Patent Application DE 10 2004 041 780.8, filed Aug. 28, 2004, the entire disclosure of which is incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to a method for electrochemical reduction of a workpiece.

BACKGROUND

For reduction, a workpiece on which a shaping or surface processing is to be undertaken by removal of material, at least in its area for processing, is brought into the environment of an electrolyte and the workpiece is placed in electrical contact with the ground. An electrode is brought into proximity with the workpiece and is shaped according to the necessary processing. A current flows through the electrolyte which is located in the intermediate space between the electrode and the workpiece being processed. An electrochemical removal of material from the surface of the workpiece occurs between this electrolyte and the workpiece due to the flow of current.

Depending on the workpiece, during the electrochemical processing, the reduction, a passivation of the surface may occur. This happens when the removal products (metal hydroxides and metal oxides) continue to adhere to the surface of the workpiece and are not transported away by electrolytes. Through the deposition of passivating materials, which form layers, the entire electrochemical potential of the process may be locally changed in the area of processing, and the reduction process, in particular the shape stability, may be influenced thereby.

Furthermore, in reduction processes, non-uniform distributions of the removal products of the workpiece in the electrolyte may occur, especially when the reduction gap between workpiece and electrode is very small, as is necessary to achieve high precision of the surface processing and the shape stability. This may result in uneven removal, and thus in deviations of the achieved shape from the desired shape of the workpiece after the processing. Furthermore, because of the deposition of removal products in the reduction gap, occasional disruptions of processing may also occur due to short circuit currents, which result in unwanted damage to the shape of the electrode and consequent processing imprecisions, but also to damage to the workpiece in the vicinity of the short circuit current.

SUMMARY OF THE INVENTION

These undesirable effects should be avoided during reduction, in order to enable very precise electrochemical processing of workpieces, such as hard-to-mill workpieces made of titanium base materials and nickel base materials.

Although the processing is described herein with regard to surface processing, it should be appreciated that the present invention may also be applied to shape-giving processing through removal of a larger quantity of the material from the surface.

An object of the present invention is to enable high processing precision by allowing the reduction gap between electrode and workpiece to have a small gap dimension, and also to reliably prevent the occurrence of depositions from passivation layers and concentrations of removal products in the electrolyte.

A device according to an embodiment of the present invention for electrochemical reduction of a workpiece includes a workpiece, an electrode, and an electrolyte that is located between electrode and workpiece. The electrode is brought close to the workpiece and held at a narrow (small) gap, and a processing of the workpiece occurs through the flow of current between electrode and workpiece through the electrolyte. In addition, a sonotrode is positioned to introduce sound waves.

The function of the sonotrode is to introduce sound waves. The sound waves in the device give rise to oscillations, in particular in the area of the electrolyte. This pulsation in the electrolyte due to the sound waves ensures that the electrolyte flows through the dimension of the gap, and therefore ensures constant transport of the removal products out of the gap. At the same time, the formation of layers of passivation on the surface of the workpiece in the area of processing is effectively prevented. Furthermore, the turbulence of the electrolyte achieves a fine distribution of the removed particles. This results in a closer tolerance of the conductivity in the entire gap and the area to be reduced thereby, so that the reduction process takes place more uniformly and effectively. The processing precision is increased.

In accordance with o an advantageous embodiment of the present invention, the sonotrode generates sound waves in the ultrasonic range, and in accordance with a further embodiment of the present invention, the frequency of the sound waves is determined in particular in such a way that no standing waves are formed in the electrolyte, particularly in the reduction gap between electrode and workpiece. The occurrence of standing waves, in particular in the reduction gap, should be prevented in order to prevent local accumulations of reduction products or exhausted electrolyte. The use of ultrasonic waves is therefore advantageous because the relatively high frequency waves enable good transport of particles to be achieved in the electrolyte.

An advantageous embodiment of the present invention provides for the sonotrode to be positioned in such a way that the radiation of the sound waves occurs in particular in the vicinity of the reduction area. This measure enables the energy of the irradiated sound waves to be kept low. At the same time, it is possible to provide both for the sonotrode to be coupled with the workpiece or the electrode and for the sonotrode to be coupled with the electrolyte. Thus the sound waves may optionally be irradiated into the workpiece, the electrode or the electrolyte, depending on the manner in which the greatest possible coupling of the sound waves into the processing area, i.e., the reduction gap, is achievable.

For example, if large-area processing of the surface of the workpiece occurs, positioning the sonotrode on the electrode may ensure that the coupling in of the sound waves takes place as close as possible to the reduction gap, regardless of how far the electrode is moved above the workpiece.

It is advantageous to couple the sound waves into the workpiece, for example, in the case of complicated shapes, when the reduction takes place in a locally defined area of the workpiece, but a deep penetration of the electrode into the workpiece occurs.

Coupling of the sound waves from the sonotrode directly into the electrolyte may be provided in particular when neither one of the previously named procedures can be carried out without great difficulties. This may be the case, for example, when a complicated spatial shape would result in limitations on the movability of the electrode by the sonotrode but at the same time a large surface of the workpiece is to be processed.

In accordance with an advantageous embodiment of the present invention, the workpiece is a metallic workpiece, in particular made of a high strength material such as a material based on titanium or nickel. With such materials, passivation layers and problems of distribution of the removal products in the electrolyte occur especially frequently. They are prevented by introducing sound waves, in particular in the ultrasonic range, by using the sonotrode, and this increases the processing precision of the workpiece during the electrochemical reduction especially advantageously.

According to the method according to an embodiment of the present invention for electrochemical reduction of a workpiece, the electrode, having a reduction gap that has a small gap dimension, is moved to above the surface of a workpiece that is to be processed, the reduction gap between electrode and surface of the workpiece being filled with an electrolyte and there being a current flowing through the electrolyte between electrode and workpiece. In addition, there is provision for sound waves to be generated by a sonotrode and coupled in.

The coupling in or introduction of the sound waves during the electrochemical reduction advantageously prevents the development of passivation layers on the surface of the workpiece in the area of the reduction gap, as well as influencing of the electromagnetic field between electrode and workpiece due to uneven distribution of the removal products in the electrolyte. This measure increases the processing precision of the electrochemical reduction, and in particular enables processing using reduction gaps having a smaller gap dimension than customary in the past.

According to an advantageous embodiment of the present invention, the sound waves of the sonotrode are coupled at least indirectly into the electrolyte, and the flow of electrolyte through the reduction gap is produced. At the same time the introduced sound waves, in particular ultrasonic waves, may support the flow of the electrolyte through the reduction gap, in particular actively, and produce a pump effect. The sound waves generated by the sonotrode are in particular ultrasonic waves, it preferably being ensured that no standing waves are formed in the electrolyte in the area of the reduction gap. It corresponds here to an advantageous embodiment if the sound waves are coupled into the electrolyte indirectly through the workpiece or the electrode. Coupling the sound waves from the sonotrode via the workpiece has the advantage in particular that the sound waves pass through the workpiece, and that the development of passivation layers in the area of the surface of the workpiece is therefore prevented in the processing area, i.e., in the reduction gap, in an especially advantageous way.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects of the present invention will be explained in greater detail below on the basis of the exemplary embodiments represented in the drawing

FIG. 1 shows a schematic representation of a device according to an embodiment of the present invention.

FIG. 2 shows a schematic representation of a device according to another embodiment of the present invention.

FIG. 3 shows a schematic representation of a device according to another embodiment of the present invention.

DETAILED DESCRIPTION

FIGS. 1 through 3 show a schematic representation of devices according to the present invention for electrochemical reduction using a sonotrode to introduce sound waves, the sonotrode being positioned in different areas.

FIG. 1 shows a schematic arrangement in which the sonotrode is positioned in the processing area of the workpiece; FIG. 2 shows an arrangement in which the sonotrode is positioned in the electrode; and FIG. 3 shows a schematic representation of an exemplary embodiment in which the sonotrode couples the sound waves directly into the electrolyte.

All three figures show a workpiece 10 which is processed by electrochemical reduction. To this end electrode 20 is guided relative to the workpiece, while a reduction gap 21 is maintained with the smallest possible gap dimension between electrode 20 and workpiece 10. In addition, there is an electrolyte 30 at least in the area of reduction gap 21. To carry out the reduction process, a current flows between electrode 20 and workpiece 10 through electrolyte 30. Because of the current, the material of workpiece 10 reacts with electrolyte 30; hydroxides or oxides of the material are forming, which are transported out of reduction gap 21 by the electrolyte and supported by the ultrasonic waves introduced by sonotrode 40.

The embodiment according to FIG. 1 shows a sonotrode 40 which is positioned in the area of workpiece 10. In contrast to that, the embodiment in FIG. 2 shows a sonotrode 40 which is positioned on electrode 20. According to these two embodiments, the sound waves generated by sonotrode 20 are coupled indirectly through workpiece 10 or electrode 20 into electrolyte 30, in particular into electrolyte 30 which is in reduction gap 21. That produces the necessary transport of removed material and the desired flow of electrolyte 30 through reduction gap 21.

According to the embodiment represented in FIG. 3, the sound waves generated by sonotrode 40 are coupled directly into the electrolyte. 

1. A device for electrochemical reduction of a workpiece, comprising: a workpiece; an electrode; an electrolyte, the electrolyte being between the electrode and the workpiece, the electrode being separated from the workpiece by a small gap dimension; and a sonotrode positioned in the device, the sonotrode generating sound waves, the device processing the workpiece via through a flow of current between the electrode and workpiece through the electrolyte.
 2. The device as recited in claim 1, wherein the sonotrode generates ultrasound.
 3. The device as recited in claim 2, wherein a frequency of the sound waves is selected so that standing waves are not formed in the electrolyte.
 4. The device as recited in one of claim 1, wherein the sonotrode is coupled to an element, the element being one of the workpiece, the electrode, and the electrolyte, and the sound waves are irradiated into the element.
 5. The device as recited in claim 4, wherein the sonotrode is positioned adjacent to an area of the workpiece that is to be processed.
 6. The device as recited in claim 1, wherein the workpiece is made of a metallic material.
 7. The device as recited in claim 6, wherein the metallic material is titanium or nickel based.
 8. The device as recited in claim 1, wherein the sound waves are introduced into a reduction area of the workpiece.
 9. A method for electrochemical reduction of a workpiece, comprising moving an electrode having a reduction gap of small gap dimension to above a surface of a workpiece to be processed; providing an electrolyte between the electrode and the surface; providing a current between the electrode and the workpiece through the electrolyte; and generating sound waves with a sonotrode.
 10. The method as recited in claim 9, wherein the sound waves are coupled into the electrolyte, and the flow of electrolyte occurs through the reduction gap between electrode and the workpiece.
 11. The method as recited in claim 10, wherein the sound waves are coupled into the electrolyte indirectly through the workpiece or the electrode.
 12. The method as recited in claim 10, wherein the sound waves are coupled directly into the electrolyte.
 13. A device for electrochemical reduction of a workpiece, comprising: a workpiece; an electrode; an electrolyte, the electrolyte being between the electrode and the workpiece, the electrode being separated from the workpiece by a small gap dimension; and a sonotrode positioned in the device to introduce sound waves into the electrolyte, the device processing the workpiece via through a flow of current between the electrode and workpiece through the electrolyte.
 14. The device as recited in claim 13, wherein the sound waves are introduced into the electrolyte indirectly through the workpiece or the electrode.
 15. The method as recited in claim 13, wherein the sound waves are introduced directly into the electrolyte.
 16. The device as recited in claim 13, wherein the sonotrode generates ultrasound.
 17. The device as recited in claim 13, wherein a frequency of the sound waves is selected so that standing waves are not formed in the electrolyte.
 18. The device as recited in one of claim 13, wherein the sonotrode is coupled to an element, the element being one of the workpiece, the electrode, and the electrolyte, and the sound waves are irradiated into the element.
 19. The device as recited in claim 18, wherein the sonotrode is positioned adjacent to an area of the workpiece that is to be processed.
 20. The device as recited in claim 13, wherein the workpiece is made of a metallic material.
 21. The device as recited in claim 20, wherein the metallic material is titanium or nickel based. 